Increasingly successful "drip" irrigation has heretofore been carried out by burying small diameter plastic pipelines in the soil with the pipelines equipped with spaced emitters that release water at minute rates. Emitters of this type now in commercial use are disclosed in copending patent applications by Theodore J. Todd, Ser. No. 60,523, filed Aug. 3, 1970 (U.S. Patent No. 3,841,349) and Ser. No. 161,838, filed July 12, 1971 (U.S. Pat. No. 3,727,635).
Typically, the emitters extend upright from the plastic pipe and each emitter incorporates two provisions to discourage the entrance of soil into its interior. One provision is a valve member that normally seats in a lower valve seat to cut off the emitter from the pipeline. When the water is turned on, the valve member rises from the lower valve seat to an upper valve seat to restrict the outflow of the emitter to a minute rate and in doing so permits the initial water flow to flush out the interior of the emitter. The second provision is that the emitter has downwardly directed discharge passages to discourage gravitation of soil and foreign particles into the emitter through the discharge passages.
Such an arrangement serves its purpose but the area irrigated by a single pipeline is limited in width to the diameter of a wet zone created by an individual emitter. To irrigate a wider area, plural parallel pipes must be used with the pipes spaced apart by no more than the diameter of a wet zone.